Electrical coils and system employing such coils



G. AW. ELMEN June 4, 1929. 1,715,542

ELECTRICAL coILs AND' SYSTEM EMPLYING SUCH lcILs Fiiedsept. 19, 1927 i Patented June 4,1929.. t l

UNITED STATES 1,115,542 PATENT OFFICE.

GUSTAF W. ELIEN, F LEONIA, NEW JERSEY, ASSIGNOB T0 BELL TELEPHONE LAB- ORA'TORIES, ICORPORTED, 0F NEW YORK.

YQBX, N; Y., A BPORATION 0l NEW ELECTRICAL COILS AND SYSTEM EHPMYING BUCH Application led September 19, 1927.y Serial lo, 230,888.

The present invention relatesto improvements in inductance coils, especially current supply and audio frequency transformers and to systems employing such transformers.-

An object of the invention is to stabllizethe inductance of magnetic coils sueh as current -supply transformers,` retardation coils, and radio transformers used in speech amplifiers. Another object isto provide that coils such as telephone repeating coils and radlo transformers will not become reduced in efficiency by the magnetic saturation of the core, but will on the contrary be made more eiective by such saturation. i

A further object is to improve telephone transmission by compensating for the dlference in attenuation of long and short lines so that subscribers connected to the central exchange by means of a long line will receive a 2o volume of speech more nearly approximating with the same central exchange by means of a short line.

The above objects are carried into effect by employing coils, or in the speciiic case,current transformers having cores of alloys which have their incremental permeability to low magnetizing forces increased when subjected to av large unidirectional magnetizing force vand after its application toland removal from the core. This is in contra-distinction to prior coils in which the incremental permea-l bility of the core is decreased by the application to and removal from the core of a large Inagnctizing force.

The term incremental permeability is used in this specification as defining the ratio of the -induction increment to the. magnetic force increment for any position on a magnetization curve, where these increments may be of any magnitude, but the magnetic force in! crement must be in the reverse direction from the immediately preceding change. See Properties and testing of magnetic materials by T. Spooner, 1927, p'a e 11. Y

Among the alloys servingt e above'mentioned purposes we may mention one consisting of approximately 45% nickel, 25% cobalt and 30% iron with a small amount of manganese added to improve the forgcability. When properly heat treated such a magnetic n composition may have, by way of example,- an initial permeability of 43.0 which remains constant up to H=1.4. When magnetized from H.=1.4 to H=1 .9 theincremental permeability increases to about 7 O0.- As the magnetizing) force is increased the incremental 1pIermea ility gradually decreases to 80 at =26. Upon decreasing' the magnetizing force the incremental permeability gradually .increases to about 700 at H= 1.9. Instead of decreasing further, the permeability actually increases to a hi her value, i. e. about 800, and then falls sligtly as the ma netizing current is reduced to zero, so that t e initial permeability is about 7 50. The important point is that the application-and removal of a large uni-directional maffnetizing force increases the incremental and initial permeabilities of the material instead of decreasing it, as in the case with well known and commonl used materials such as Armco iron.

The present application is in .part a con# tinuation of application Serial. No. 119,622,

y led June 30, 1926. the volume received by a subscriber connected It has been found that a large class of alloys of cobalt, nickel and iron, with or without other ingredients, exhibit the property of increased permeability at small magnetizations circuiting or to any` other cause of large uni-directional magnetizing force. The invention comprises broadly the application of any magnetic material exhibiting this property to such purposes as cores of current supply transformers, audio frequency transformers, retardation coils, or any coil or transformer which might become subjected to short-circuiting or to any other cause of large currents. l

In applicants copending applications, Serial No. 119,622, filed June 30, 1926, and Serial No. 220,387, `filed September 19, 1927, there are disclosed and claimed various ma netic compositions containing nickel, coba, and iron with or without a fourth element such as molybdenum or chromium for increasing the resistivity and lessening the eddy cure rent losses. A particular composition containing such a fourth element is one Acomprising approximately 50% Ni, 25% Co, 211/2% Fe and S31/2% Mo.v This composition exhibits satisfactory properties. acterized by an incremental `permeability variation such as that of the particular compositions mentioned therein may be employed with great'advanta-.ge as cores for inductance and other coilsin accordance with the present invention. `In general magnetic compositions containing cobalt between 5 and 80%, nickel between 20 and 81%, and'iron between -9 and Compositions cha-r-P 50%, with or without the addition of up to about 8% of a fourth element to increase the resistivity, exhibit to some extent properties suitable for the purposes herein described. The best compositions are those having a content of the several elements somewhat within the extremesof the ranges cited. The compositions of nickel content from about to' 75% exhibit, in general, the higher values of greater detail in connection with the accompanying drawings, in which;

Fig. 1 represents the variation of permeability with increasing direct current magnetizing forces of a sample material of the present invention, as compared with Armco iron, a small alternating current being superimposed in each case; l

Fig. 2 depicts a portion of the apparatus at a telephone central oihce, namely, a current supply coil in a connecting cord circuit having a core made of a magnetic material in accordance with the invention, in conjunction with telephone lines of different lengths; and

Fig. 3 shows a portion of an' audio frequenc transformer including cores of the material described herein.

f Curve A of Fig. 1 depicts the permeability variation of anA alloy containin approximately Ni, 30% Fe, 23% o and .5%

Mn when an alternating magnetizing force or" .00207 gauss is impressed upon a variable uni-'directional magnetlzing force. The inis tial permeability vwas about 430. As the unidirectional magnetizing force was increasedfrom I0 to 1.7 the permeability remained sub'- fstantially constant, but at a magnetiaing -orce between 1.7 and 1.9, the permeability increased suddenly to over 700, andwith furi ther increase of the magnetizing force diminished steadilyl until at about 26 ganse the permeability was about 40. Removal ofthe' uni-directional magnetizing force, however,

Y meability with increasing direct current magnetizing forces for Armco iron when an .alternating currentof .00532 am eres is s uhe 1nit1al perimposed upon the circuit.

permeability of thismaterialis seen to be about 200. As the uni-directional magnetizing force increases, the permeability diminlshes rapidly for the first 3 gauss, andthen less rapidly as the magnetizingforces are further increased'. The removal of the magnetizin force ,does not tend to restore the permea ility to its primary state, but on the contrary, at zero magnetizingforce the permeability is only' about 50.

We shall now consider Fig. 2 in conjunction with the permeability variations :discussed 1n Fig. y1. .In Fig. 2 we have anarrangcment comprising current supply re' peating coil A having primaryvwinding 1, secondary winding 2 and core 3, and vbattery 4. By means of plug 5 and jacks 6 and .7 the current supply coil-maybe connected either to line 8 or line 9. 'Line 8' is assumed'to have a length of 5 miles land line 9 a length of 20 miles. B indicates a subscribers station at the end of line 8 and C a subscribers station at the end of line 9. When the shorterline 8 is being used for telephone service adirect current traverses the circuit constituted by the battery 4, the current supply'coil A and line 8. Assume that the parts are so roportioned tha this direct current estab ishes a .direct curr nt field of 24e. g. s. units, superimposed upon the alternating current which is set up by the fluctuating signaling curphone service to current supply coil A. Since the length of this line is'20 miles, it offers a considerable resistance to'the flow of the direct current supplied by battery 4. The intensity of this direct current', therefore, will bel decidedly lower, as will also be that of the magnetic field set up in the core 3 by this produced by thef-direct'current is f4 gauss. Inspection 'of Fig. 2 shows that the permeability of the material for, the magnetizingv force due to the voice currents is approximately 600 in this case. The cases which we current. Suppose that the magnetizing `force have assumed are quite in accordance with practical conditions. j

With installations of this type used at the present time the maximum direct current which will pass -through the windings of the battery supply coilwill produce ,a direct current magnetizing force ofabout 26 gauss. A i

material which is in common use in these cores is Armco 1ron. After' the appllcatlon of a magnetizing force of 26kg'auss the pery meability. of the Armco iron ispreduced from an initial value of about 200 in the virginmaterial vto' about -50 after the ield has been' applied and removed. lThis is a rather low" -permeability';for' the .functions which these cores have toA perform. By comparison with v and 40 and battery 60. 20.

Vthe incremental `permeability of 6 00 of the alloy herein described the advanta e of their use 'as current supply coil cores w' l be easily appreciated. f 1

Fig. 3 shows, as a further example of practicing the present invention, a portion of an audio-frequency amplifier. Detector 20 is designed for detectin received radio signaling waves, transformmg them into electrical waves of audible frequency Y and aptplying them to the input connections of trans ormer 30. Transformer 30 steps up the voltage ofv the signal waves and impresses it upon vacuum tube amplifier 31, which in turn, after further amplification, impresses the waves upon the input circuit of transformer 40. A choke coil 50is inserted into the circuit between the primary windin s, transformers 30 e cores of transformers 30 and 40 and coil 50 are composed of material in accordance with the present'inv vention. Assume, no w that for any reason, such as a temporary short circuit, the direct' 'current passing through the windin s of transformers .30 and 40, or coil 50, or oth, is considerably if This large current will set u a cbr'respondingly high unidirectional ie d in the core material of the transformers 30 and 40 and of the choke coil '50. If the core material is Armcoiron or a similar composition, the permeability after the cessation of the excessive current will be decreased from a value around 200 `to a value around 50. If, however, material in accordance with this invention is em loyed for forming the cores of the coils, in a dition to the advantage-ofV considerably higher permeability to start with (around 450 'or more),

the large current actually raises the permeability of the material after the removal of the current.

In orderto produce the magnetic roper- `Vyties desirable and useful for the app ication of the materials' of the present invention for thel purposes intended the material must be properl heat-treated after allthe mechanical wor incident to its manufacture has been completed. The magnetic particular composition o e alloy are largely dependent u For which was conducive of 4good results consisted in heating material to about 1100` C. for' approximately one hour and then cooling it ncaling temperature to room temperature. l s

preperties of any n this heat treatment and especially upon t e rate of coo the composition containing approxu'natelyA 45% Ni25% Co and 30% Fe, a .treatment A treatment comprising reheatin the slowly I cerning eat treatments and descriptions of other specific alloys suitable forpresent purposes are'disclosed in the applications mentioned above.

'Satisfactory results werev obtained for a composition containing approximately 50% Ni, 25% Co, 211/% Fe and itl/2% Mo by tannealing the alloy at about 1100 C. for a ut one hour and then l'cooling it slowly in the furnace down to room temperature.

What is claimed is:

1. vA coil having a core characterized by incremental permeability at low magnetizing forces vgreater after being subjected to a large direct magnetizing force than priory thereto.

2. A transformer having acore of incremental permeability-higher at small or moderate magnetizing forces after being sub- 'ected to a large D. C. magnetizin force than efore the application of said netizing force.

3. A current supply transformer compris;v

ing a core composed of lmagnetic material comprising cobalt between 5% and 80%,A

tivity between a small value and about 8%.

` '5. A coil having a core of nickel between A.40% and 7 5%, cobalt between 15% and 50%,'

iron between 15% and 40%.-

6, A coil having a core composed of inag-A 'rect magan additional element to increase the resisnetic material com rising as essential elements approximate balt'and 30% iron.

7. A current supply repeating coil com rising a primary win in a secondary win anda core, said core y 45% nickel, 25% cogreater when subjected to a large direct ma netizing force than when subjected to a ama er direct magnetizing force.

GUSTAF w. ELMEN. f

ing characterized by'. incremental permeability for' voice currents 

